1. Field of the Invention
The present invention relates to a registration apparatus, a collation apparatus, an image correction method and a program that can suitably be used in applications for biometric authentications.
2. Description of the Related Art
Blood vessels have been objects of biometrics authentication among others. Generally, authentication apparatus include an image pickup camera and a finger is typically rigidly secured in position in parallel with the imaging plane of the image pickup camera in order for the camera to shoot blood vessels in the finger. The authentication apparatus then registers the image of the blood vessels obtained as a result of the shooting operation in a memory or the like or compares the image with the image of blood vessels registered in a memory or the like to identify the person to be identified.
However, when shooting blood vessels in a finger, it is neither convenient nor comfortable for the person to be identified to rigidly secure the finger on the image pickup camera. In other words, there is a demand for arrangements allowing the person to place a finger on an image pickup camera without restrictions from the viewpoint of user friendliness.
On the other hand, when an image pickup camera shoots blood vessels placed on the camera without restrictions, the condition in which the finger was placed on the camera when the image of the blood vessels was registered and the condition in which the finger is placed on the camera for authentication can highly probably be different from each other.
In practical applications, one of the typical instances where the condition of a finger differs between at the time of registration and at the time of authentication is the angle between the imaging plane of the image pickup camera and the finger placed on the camera, or the inclination of the finger relative to the imaging plane.
When an image of blood vessels of a finger is picked up in a condition where the finger is inclined relative to the imaging plane of the camera, the finger in the image picked up for the blood vessels shows a profile that is long at a part located close to the image pickup camera and short at a part located remote from the image pickup camera. In short, the picked up image of the finger is distorted.
If the distortion of the finger in an image thereof (distortion of projection) differs between the time of registration and the time of authentication, there can arise a case where the finger is that of a registered (authorized) person but determined to be that of an unauthorized (unregistered) person and a case where the finger is that of an unauthorized (unregistered) person but determined to be that of a registered (authorized) person. In short, the accuracy of authentication will be poor.
To dissolve the problem of distortion of projection, there are known techniques of correcting an image of an object to be authenticated by making the length of the part of a profile thereof located closer match the length of the part of the profile located nearer to the image pickup camera or vice versa (see, for example, Jpn. Pat. Appln. Laid-Open Publication No. 2000-22869 (FIGS. 11 and 12).